Foam dispensers fall into two general categories: hand-held squeeze bottles and foam aerosols. Hand-held squeeze bottles are non-aerosol foam dispensers. When squeezed, foam is produced by the mixing of flowing streams of foamable liquid and air in a distinct mixing area. Foam is produced when these flowing streams are absorbed into a sponge-like foam producing element. The hand-held squeeze bottles typically use a different path for air reentry into the bottle than the path used for dispensing foam. These bottles have drawbacks, however, because they are designed to be handheld operated and must therefore be limited in size. Hand-held squeeze bottles also suffer from the disadvantage that the foamable liquid can leak out of the bottle if the bottle is not held upright. Another common disadvantage of the hand-held squeeze bottles is that they fail to replenish the reservoir bottle with adequate amount of air. As a result, the reservoir has a disproportionate amount of foamable liquid to air and is, therefore, unable to produce suitable foam.
For example, U.S. Pat. No. 5,033,654 to Bennett discloses a foam dispenser having a deformable reservoir of foamable liquid and air and a foam producing segment that includes a foam filter. When the foam dispenser is operated, air from the inside of the reservoir mixes with the foamable liquid to produce foam. To replenish air back into the reservoir after foam has been dispensed, a check valve in the form of a moving ball within a cylinder is used. The check valve is disposed outside the foam's flow path. The patent discloses that when the deformable reservoir is squeezed, the walls of the reservoir bottle collapse causing air in the reservoir to push the ball against one end of the cylindrical thereby obstructing the passage of air from the check valve. Immediately after dispensing foam, during the so-called relaxation stage, the elastic walls of the reservoir bottle revert back to their original shape and create a relative vacuum. The back pressure causes the ball of the check valve to drop from one end of the cylindrical housing to the other end allowing ambient air to replenish the reservoir. Because the plastic container used as the reservoir is relatively weak, it can only offer modest restorative forces. For example, a typical container may be able to create as little as 0.5 psi of vacuum as it returns to its original shape. In addition, once the ball is seated against the end of the cylindrical housing, the air path into the reservoir is at least partially obstructed. As a result, this and similar designs fail to timely and adequately replenish the reservoir with air. The relatively slow re-fill, or replenishment of air, fails to return the bottle to its original size. Consequently, most of its volume may consist of liquid. The next squeeze produces improper air/fluid ratio thus degrading the quality of foam, and in worst cases, only liquid (thus no foam). In the absence of an adequate amount of air in the reservoir foam production will be hampered.
Another important requirement of the air refill method is the effectiveness during the dispensing stroke. If during dispensing stroke air escapes from the refill passage, then less foam would be produced and dispensed.
Aerosol foam dispensers overcome only some of the problems of hand-held squeeze bottles. In foam aerosols, pressurized hydrocarbon gases, and in the past fluorocarbon gases as well, drive the active substances out of a reservoir. Aerosols, however, have other drawbacks. Fluorocarbons have been rejected for environmental reasons and hydrocarbons are unsafe due to inflammability. Safe propellants aimed at remedying these concerns include compressible gases such as nitrogen or compressed air. These safe propellants, however, are not as dissolvable in liquid active substances as hydrocarbons. This makes it difficult with these safer propellants to keep the pressure sufficiently high and maintain effective spraying as the active substances are consumed. Moreover, it is difficult with such propellants to obtain useful aerosol foams from conventional valve and dispenser head combinations.
Thus, there is a need for foam dispenser that can provide timely and effective air refill while providing a hermetic seal during storage and transport.